1. Field of the Invention
This invention relates to a low-voltage circuit breaker that has a carrier mounted on a control shaft and connected to a movable contact by means of a contact pressure spring and further provided with a toggle lever system connecting the operating handle and the carrier to separate the movable contact from the fixed contact in response to actuation of the operating handle. In particular, the invention relates to such a circuit breaker including a locking lever pivotably mounted in the housing of the circuit breaker and engaging the handle to be moved thereby and provided with means to engage the carrier when the handle is moved toward the "off" position if the carrier is locked on its "on" position by welding of the fixed and movable contacts together.
2. Prior Art
A circuit breaker generally similar to the present invention is shown in U.S. Pat. No. 4,165,453, in which a locking lever of a two-arm design is pivoted about a bearing formed by the toggle joint pin of a toggle lever system connected to the movable contact part of the circuit breaker. One of the lever arms of the locking lever is inside the turns of a drive spring that would normally separate the movable contact from the fixed contact when the actuating arm of the circuit breaker was moved to its "off" position. The other lever arm of the toggle system rests against the movable contact part of the circuit and, specifically, against the joint pin that establishes the connection of the toggle lever system with the movable contact portion. If the movable contact is blocked in the "on" position, for example, because of having the contact overlays of the stationary and movable contacts welded together, a force is exerted when an attempt is made to move the operating handle of the circuit breaker in the direction of its "off" position. This force is transmitted by the locking lever onto the toggle joint pin of the toggle lever system, which causes the latter to buckle in the direction of the "off" motion. However, the operating handle cannot be moved completely into its "off" position unless the force exerted on the toggle lever system is sufficiently large to break the contact weld.